1. Field of the Invention
This invention relates to an electronic apparatus, and particularly to an apparatus for effecting electric power supply to an apparatus connected thereto.
2. Related Background Art
With the spread of personal computers, digital cameras, etc., the higher definition of recording apparatuses such as printers for recording image data of a digital type has been advanced. Among the recording apparatuses, an ink jet recording apparatus using a recording head of an ink jet type has rapidly spread, and there is demand for one which realizes images of high definition and is low in price.
In an ink jet recording apparatus of a serial scan type, Recording is effected while a recording head is scanned in a direction (main scanning direction orthogonal to the conveying direction of a recording medium such as recording paper, and at a stage whereat one scan of recording has been finished, the recording medium is conveyed, and by the repetition thereof, an image is formed.
In recent years, user's demand for printing in a recording apparatus directly from a digital camera without the intermediary of a host computer has become high, and the direct printing function of effecting print directly from an apparatus provided with an image pickup element such as a digital camera onto a recording apparatus has become a function necessary for the recording apparatus.
Heretofore, in a recording apparatus supporting the direct printing function, USB has been used as an interface. One of the features of USB is that it can supply a power source from a host side to a peripheral device (USB device) through a USB cable. The supplied electric current is 500 mA at maximum per peripheral device. There has been adopted a construction in which the recording apparatus is provided with the function of a USB host and, it is connected to a digital camera as a USB device (function), but connectable digital cameras have been restricted. These connectable digital cameras have been of the so-called self power type operable even without a power source being supplied from the USB host.
Therefore, as the recording apparatus, it has been enough if it has the capability of supplying an electric current of 100 mA or less to Vbus which is the power supply line of USB. Also, if the connected USB device has pulled up 100 mA or greater from the Vbus, it has been detected that 100 mA or greater has been pulled up, and the Vbus has been forcibly disconnected. The electric current supplied by the Vbus is small, and therefore, a load to the power source of the recording apparatus is light. Accordingly, in a case where a digital camera is connected to the USB host and in a case where a digital camera is not connected to the USB host, there has not occurred the necessity of changing a printing mode (recording mode) or the like for the reason of the load of the power source.
Also, in order to reduce the cost of a power supply device (power supply circuit), there has been the technique of effecting the control of a recording operation in conformity with recording data. For example, a recording duty (the value of a recording duty) is detected and is compared with a preset duty value to thereby change the recording operation. Thereby, the balance between the throughput of recording and the cost for the power supply is kept.
In recent years, however, cases where a bus power device activated by being supplied with a power source from the USB host is connected are increasing due to the diversification of USB device to be connected. Therefore, the power source capacity which must be supplied from the Vbus of a USB interface has increased. Specifically, maximum 500 mA must be capable of being supplied. In order to solve this problem, the capability of the power source of the recording apparatus can be increased, but this will result in a power source of high cost. In other words, how 500 mA can be supplied to the Vbus while the cost of the recording apparatus is suppressed is a task.